Celyn Eadon of Derrycrieve, Islandeady, Castlebar admits killing Noreen Kelly at that address on March 9, 2011. He has pleaded not guilty to murdering the 46-year-old, but guilty to her manslaughter.

On the opening day of his trial at the Central Criminal Court, the jury heard that Mr Eadon was using drugs at the time of his mother’s killing.

Isobel Kennedy SC, prosecuting, said his younger brother heard him shouting at their mother after she threw a bag of white powder into the fire.

She said garda tests on three charred plastic bags recovered from the fire showed they contained methamphetamine.

The court also heard from recovered drug addict Kevin Mitchell, who had been asked to help the accused.

He said by Mr Eadon’s uncle, Patrick Kelly, had first brought him to meet his nephew a few days before the killing.

“He was pretty scared, hallucinating, walking around the forest, seeing fire-ants coming for him and demons,” he testified. “I felt it was very serious, like his mind was going.”

He said he told the accused about a place where he could get treatment and tried to make an appointment for him.

He said he also told the deceased that her son badly needed help.

“His mind was snapped to me. I told her he was on drugs,” he recalled. “He was on speed. He offered me speed when I got there.

“I told her it would be dangerous to throw drugs in the fire. I knew by the way he was, it could be a bad move. I could see he was hallucinating,” he recalled. “If he was coming down off stuff and his drugs were missing, he could go crazy. It could manifest in violence.”

He agreed with Diarmaid McGuinness SC, defending, that the deceased called him and Mr Kelly to the house again a few days later.

“She said Celyn had poured petrol inside and outside, and was going around with a hatchet,” he said.

He said that the accused would not come out of the shower to speak to them for a long time and that his mother said he had been spraying deodorant into the air to try to kill demons.

“I knew he was on drugs the second day. It was obvious,” he said.

He agreed with Mr McGuinness that he would associate the hallucinations his client was having with drug taking, and that it was one of the worst cases he had ever seen.

He said the accused had calmed down when they left that evening, but was still not well.

The court heard that later that night, the sound of muffled screaming woke Mr Eadon’s younger brother.

“It was the voice of his mother,” said Ms Kennedy in her opening speech. “He found his mother slumped on the living room floor, her face covered in blood.”

A post-mortem examination found she died of multiple stab wounds.

The trial continues before Mr Justice Paul Carney and a jury of seven men and five women.